A conventional semiconductor device is known in which a through plug (a through plug) is provided to a Si substrate for highly densifying wirings.
There is a semiconductor device in which a through plug is connected to an upper wiring via a contact plug formed on a Si substrate. The semiconductor device, for example, is disclosed in JP-A 2007-123857. When a through plug is connected to an electrode pad formed on a Si substrate, there is a possibility that the electrode pad is removed due to overetching when a contact hole for the through plug is formed on the Si substrate, however, since the contact plug is thicker than the electrode pad, it is less likely to be removed even if etching reaches the contact plug.
However, when the etching reaches the contact plug, there is a possibility that etching damage is generated on a bottom surface of the contact plug and the contact plug is not appropriately connected to the through plug, which may result in an increase in electrical resistance at a connection. Furthermore, there is a risk that the contact plug does not electrically conduct to the through plug.